1. Field of the Invention
The present invention relates to a method and apparatus for determining the number of distribution nodes necessary to provide Very High Speed Digital Subscriber Line (VDSL) services to subscribers.
2. Related Art
Conventional modulator-demodulators (xe2x80x9cmodemsxe2x80x9d ), have traditionally been used in home and small business personal computers (PC""s) to connect to the Internet over telephone lines. Such modems modulate the digital signals from a computer into analog signals, more specifically modulated tones in the voice-band (DC to 4 KHz) that can be sent over telephone lines through the Public Switched Telephone Network (PSTN), and demodulate incoming analog signals back into digital signals that the computer can process them. However, due to the bandwidth limitations imposed by bandpass filters and codes at PSTN interface points, traditional modems have, for all practical purposes, reached their speed limit with the introduction of the 56 Kbps models.
The above-mentioned speed limitations of traditional voice-band modems make such modems less than satisfactory for meeting the demand for downloading graphic intensive Internet web pages and other information, and even worse for the type of two-way information transfer required for video conferencing. In recent years, several options have been introduced for providing broadband access at speeds significantly higher than voice-band modems. Among the high speed options available are T1 and cable lines. However, each of these technologies requires that specialized wiring be installed at the subscribers location, at a cost that may be prohibitive to home and small business users.
Among the newest high-speed alternatives is Digital Subscriber Line (DSL) technology. DSL uses a subscriber""s existing copper POTS (xe2x80x9cplain old telephone systemxe2x80x9d) lines to gain access to the Internet and other high-speed data and video servicesxe2x80x94up to 55 Mbps. Thus, DSL offers the advantage of making use of lines already connected to the subscriber, but with speeds exceeding T1 and cable lines.
The use of DSL requires the presence of a DSL modem at the subscriber and a counterpart at the service provider, usually the local telephone company, connected by a twisted pair copper telephone line. DSL modems send and receive data, over POTS lines, in a frequency range that is higher than the voice-band, and which permits much higher data rates. And because voice-band modem transmissions and voice calls use only a portion of the available bandwidth of the POTS line, a subscriber can carry on a telephone conversation, or use a voice-band modem, while at the same time operating a DSL modem.
One factor that must be taken into account in applying DSL technology is that the twisted pair subscriber lines have distortion and losses that increase with frequency and line length. Thus, for DSL to work properly, there is a limit to the line length between a subscriber""s DSL modem and the phone company""s answering DSL modem, the permissible line length decreasing the higher the data rate offered over the line. To account for this limitation, DSL providers must limit the length of the copper line over which the DSL signal is transmitted.
FIG. 1 shows a conventional method for sending a basic telephone signal from the telephone company""s central office to the subscriber via twisted pair copper telephone lines. As shown in the figure, some subscribers, such as those having telephones 106, have twisted pair lines 104 connected directly to the central office (CO) 100. Other subscribers have their telephones 110 connected to the CO 100 through a cross connect 102. The use of the cross connect 102 makes it practical to connect a larger number of subscribers to the CO 100, and most CO""s are large enough so that over 80% of the twisted pairs are connected through cross connects.
The telephone network was originally designed to provide voice-band telephone service up to 4 KHz. In order to provide VDSL services, operating typically at a much higher frequency than voice-band signals, the subscriber copper line may have to be less than 2500 feet, which is the typical range of present VDSL modems. Since subscribers may be located over 12,000 feet from the central office or cross connect, the telephone company""s VDSL modem is placed within 2500 feet of the subscriber and connected to the CO by means of an optical fiber. Although the figure of 2500 feet will be used throughout the specification as the critical length, that length may vary depending upon the data rate, wire gauge, and other factors.
FIG. 2 shows the basic method for connecting DSL lines to subscribers. Elements in common with FIG. 1 will be assigned the same reference numerals as in that figure.
As shown in FIG. 2, VDSL NODE 1112, comprising a VDSL modem present at the CO 100, is connected directly via twisted pairs 104, to subscribers using telephones 106, each of which is less than 2500 feet from the CO 100. On the other hand, twisted pairs 108, associated with telephones 110, each are connected to the CO 100 via cross connect 102 and are at a distance greater than 2500 feet from the CO 100. To supply VDSL service to these subscribers, an optical line 114 is run to a VDSL NODE 2116 located within 2500 feet of each of the subscribers. The information to be supplied to the subscribers is sent as an optical signal via the optical line 114 to the VDSL NODE 2, converted into an electrical signal and supplied to the twisted pair lines 108 for distribution to the subscribers.
FIG. 3 shows a typical distribution of twisted pairs from a cross connect 200 to the subscriber. In the figure, pairs 1-26 supply service to Main Street. Pairs 27-50 supply service to Grove Street. Pairs 51-61 supply service to Joy Street, and pairs 62-70 supply service to Alice Street. In a layout such as is shown in FIG. 3, the trunk telephone cable would typically run along Main Street, with branch cables being separated from the trunk cable for side streets such as Grove Street, Joy Street and Alice Street.
As can be seen from the distance indications on FIG. 3, the layout includes pairs that are more than 2500 feet in line length from the cross connect 200. Thus, assuming the cross connect itself has a node supplied directly from the CO, additional VDSL nodes would be needed to supply pairs more than 2500 feet from the cross connect.
In the layout of FIG. 3, it can be discerned by visual inspection that a node, supplied by optical cable, would have to be installed at the cross connect 200 to supply pairs located at a line length less than 2500 feet from the cross connect 200. A node placed at a cross connect will be referred to hereinafter as a xe2x80x9cfirst levelxe2x80x9d node. However, since a number of the pairs shown in the figure are located more than 2500 feet in line length from the cross connect, additional node or nodes, to be referred to hereinafter as xe2x80x9csecond levelxe2x80x9d nodes, will be necessary to supply those pairs.
For example, it appears from a cursory examination of FIG. 3 that a second level node would have to be placed on Main Street at a line length 2500 feet from the cross connect to supply pairs on Main Street located at a line length more than 2500 feet from the cross connect 200, another second level node placed on Grove Street at a line length 2500 feet from the cross connect to supply pairs on that street that are located at a line length more than 2500 feet from the cross connect, and yet another second level node placed on Alice Street to supply pair 66, which is located at a line length more than 2500 feet from the cross connect.
FIG. 3 shows a layout of only a small number of streets. In actual street layouts, which for a particular CO may have over 100 cross connects, each having over 1000 pairs, calculation of the number of branches containing pairs having a line length longer than 2500 feet (hereinafter xe2x80x9cbranches of interestxe2x80x9d) can take many weeks. Further, even if it is determined how many such branches are present, it may not be strictly necessary to provide a dedicated second level node to each branch. That is, it may be possible to further reduce the number of nodes by having some of the branches of interest share a second level node. This complicating factor makes it even more difficult to quickly provide an accurate estimate of the number of nodes that may be needed to service a given area, even after the number of branches of interest have been determined.
Thus, there exists a need for a method and apparatus for quickly and accurately calculating the number of branches of interest and of estimating the minimum number of VDSL nodes necessary for any given street layout.
It is an object of the present invention to provide a method of estimating, for a given twisted pair layout, the number of VDSL nodes necessary to supply service to subscribers connected via the twisted pairs, and to do so much more quickly than prior art methods.
In accordance with one aspect of the present invention, there is provided a method for estimating a number of digital subscriber line nodes required to supply, from a line supply source, a geographically distributed network of substantially sequentially numbered twisted pair lines with digital subscriber line service. The method comprises the steps of: storing, in number order, data entries for every twisted pair line of the network, each data entry comprising a pair number and a line length of the respective twisted pair line in relation to the line supply source; sorting the entries stored in the database by line length; isolating those sorted entries having a line length greater than a predetermined maximum line length in relation to the line supply source; sorting the isolated entries by number; and discriminating, from the sorted isolated entries, a number of discrete groupings of substantially contiguous entries. The number of required line nodes is equal to one plus the number of discrete groups, other than a first such group, that are separated in line number from an immediately previous group by more than a predetermined number. Preferably, the predetermined number is calculated based upon an area density of subscribers in the geographically distributed network.
In accordance with another aspect of the present invention, there is provided an apparatus structured to estimate a number of digital subscriber line nodes required to supply, from a line supply source, a geographically distributed network of substantially sequentially numbered twisted pair lines with digital subscriber line service. The apparatus comprises: means for storing, in number order, data entries for every twisted pair line of the network, each data entry comprising a pair number and a line length of the respective twisted pair line in relation to the line supply source; means for sorting the entries stored in the database by line length; means for isolating those sorted entries having a line length greater than a predetermined maximum line length in relation to the line supply source; means for sorting the isolated entries by number; and means for discriminating, from the sorted isolated entries, a number of discrete groupings of substantially contiguous entries. The number of required line nodes is equal to one plus the number of discrete groups, other than a first such group, that are separated in line number from an immediately previous group by more than a predetermined number. Preferably, the predetermined number is calculated based upon an area density of subscribers in the geographically distributed network.
In accordance with yet another aspect of the present invention, there is provided a computer-readable storage medium storing code executable on a processor-controlled apparatus to cause the apparatus to perform a method for estimating a number of digital subscriber line nodes required to supply, from a line supply source, a geographically distributed network of substantially sequentially numbered twisted pair lines with digital subscriber line service. The method comprises: storing, in number order, data entries for every twisted pair line of the network, each data entry comprising a pair number and a line length of the respective twisted pair line in relation to the line supply source; sorting the entries stored in the database by line length; isolating those sorted entries having a line length greater than a predetermined maximum line length in relation to the line supply source; sorting the isolated entries by number; and discriminating, from the sorted isolated entries, a number of discrete groupings of substantially contiguous entries. The number of required line nodes is equal to one plus the number of discrete groups, other than a first such group, that are separated in line number from an immediately previous group by more than a predetermined number.
Preferably, the predetermined number is calculated based upon an area density of subscribers in the geographically distributed network.
In accordance with still another aspect of the present invention, there is provided a system for calculating a number of digital subscriber line nodes required to supply, from a line supply source, a geographically distributed network of substantially sequentially numbered twisted pair lines with digital subscriber line service, the system comprising: a digital storage circuit that stores, in number order, data entries for every twisted pair line of the network, each data entry comprising a pair number and a line length of the respective twisted pair line in relation to the line supply source; and a digital logic circuit operable to interface with the digital storage circuit to: sort the entries stored in the digital storage circuit by line length; isolate those sorted entries having a line length greater than a predetermined maximum line length in relation to the line supply source; sort the isolated entries by number; and discriminate, from the sorted isolated entries, a number of discrete groupings of substantially contiguous entries. The number of required line nodes is equal to one plus the number of discrete groups, other than a first such group, that are separated in line number from an immediately previous group by more than a predetermined number. Preferably, the predetermined number is calculated based upon an area density of subscribers in the geographically distributed network.
In accordance with another aspect of the present invention, there is provided a method for calculating a number and location of digital subscriber line nodes guaranteed to supply, from a line supply source, a geographically distributed network of substantially sequentially numbered twisted pair lines with digital subscriber line service. The method comprises the steps of: storing, in number order, data entries for every twisted pair line of the network, each data entry comprising a pair number and a line length of the respective twisted pair line in relation to the line supply source; sorting the entries stored in the database by line length; isolating those sorted entries having a line length greater than a predetermined maximum line length in relation to the line supply source; sorting the isolated entries by number; and discriminating, from the sorted isolated entries, a number of discrete groupings of substantially contiguous entries. The number of nodes is equal to the discriminated number of discrete groups and the nodes are located at the twisted pair from among each discrete group having the shortest line length.
In accordance with another aspect of the present invention, there is provided apparatus structured to calculate a number and location of digital subscriber line nodes guaranteed to supply, from a line supply source, a geographically distributed network of substantially sequentially numbered twisted pair lines with digital subscriber line service. The apparatus comprises: means for storing, in number order, data entries for every twisted pair line of the network, each data entry comprising a pair number and a line length of the respective twisted pair line in relation to the line supply source; means for sorting the entries stored in the database by line length; means for isolating those sorted entries having a line length greater than a predetermined maximum line length in relation to the line supply source; means for sorting the isolated entries by number; and means for discriminating, from the sorted isolated entries, a number of discrete groupings of substantially contiguous entries. The number of nodes is equal to the discriminated number of discrete groups and the nodes are located at the twisted pair from among each discrete group having the shortest line length.
In accordance with yet another aspect of the present invention, there is provided a computer-readable storage medium storing code executable on a processor-controlled apparatus to cause the apparatus to perform a method for calculating a number and location of digital subscriber line nodes guaranteed to supply, from a line supply source, a geographically distributed network of substantially sequentially numbered twisted pair lines with digital subscriber line service. The method comprises: storing, in number order, data entries for every twisted pair line of the network, each data entry comprising a pair number and a line length of the respective twisted pair line in relation to the line supply source; sorting the entries stored in the database by line length; isolating those sorted entries having a line length greater than a predetermined maximum line length in relation to the line supply source; sorting the isolated entries by number; and discriminating, from the sorted isolated entries, a number of discrete groupings of substantially contiguous entries. The number of nodes is equal to the discriminated number of discrete groups and the nodes are located at the twisted pair from among each discrete group having the shortest line length.
In accordance with still another aspect of the present invention, there is provided a system for calculating a number and location of digital subscriber line nodes guaranteed to supply, from a line supply source, a geographically distributed network of substantially sequentially numbered twisted pair lines with digital subscriber line service. The system comprises: a digital storage circuit that stores, in number order, data entries for every twisted pair line of the network, each data entry comprising a pair number and a line length of the respective twisted pair line in relation to the line supply source; and a digital logic circuit operable to interface with the digital storage circuit to: sort the entries stored in the digital storage circuit by line length; isolate those sorted entries having a line length greater than a predetermined maximum line length in relation to the line supply source; sort the isolated entries by number; and discriminate, from the sorted isolated entries, a number of discrete groupings of substantially contiguous entries. The number of nodes is equal to the discriminated number of discrete groups and the nodes are located at the twisted pair from among each discrete group having the shortest line length.